| Arabidopsis thaliana | |
|---|---|
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Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Brassicales |
| Family: | Brassicaceae |
| Genus: | Arabidopsis |
| Species: | A. thaliana |
| Binomial name | |
| Arabidopsis thaliana | |
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The range ofArabidopsis thaliana.
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| Synonyms[1] | |
Arabis thaliana | |
Arabidopsis thaliana, thethale cress,mouse-ear cress orarabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa.[2][3][4][5][6][7] Commonly found along the shoulders of roads and in disturbed land, it is generally considered a weed.
Awinter annual with a relatively short lifecycle,A. thaliana is a popularmodel organism inplant biology and genetics. For a complex multicellulareukaryote,A. thaliana has a relatively smallgenome of around 135megabase pairs.[8] It was the first plant to have its genome sequenced, and is an important tool for understanding themolecular biology of many plant traits, including flower development andlight sensing.[9]
Arabidopsis thaliana is anannual (rarelybiennial) plant, usually growing to 20–25 cm tall.[6] Theleaves form a rosette at the base of the plant, with a few leaves also on the floweringstem. The basal leaves are green to slightly purplish in color, 1.5–5 cm long, and 2–10 mm broad, with an entire to coarsely serrated margin; the stem leaves are smaller and unstalked, usually with an entire margin. Leaves are covered with small, unicellular hairs calledtrichomes. Theflowers are 3 mm in diameter, arranged in acorymb; their structure is that of the typicalBrassicaceae. The fruit is asilique 5–20 mm long, containing 20–30seeds.[10][11][12][13] Roots are simple in structure, with a single primary root that grows vertically downward, later producing smallerlateral roots. These roots form interactions withrhizosphere bacteria such asBacillus megaterium.[14]
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A. thaliana can complete its entire lifecycle in six weeks. The central stem that produces flowers grows after about 3 weeks, and the flowers naturally self-pollinate. In the lab,A. thaliana may be grown in Petri plates, pots, or hydroponics, under fluorescent lights or in a greenhouse.[15]
The plant was first described in 1577 in theHarz Mountains byJohannes Thal [de] (1542–1583), a physician fromNordhausen,Thüringen, Germany, who called itPilosella siliquosa. In 1753,Carl Linnaeus renamed the plantArabis thaliana in honor of Thal. In 1842, German botanistGustav Heynhold erected the new genusArabidopsis and placed the plant in that genus. Thegeneric name,Arabidopsis, comes fromGreek, meaning "resemblingArabis" (the genus in which Linnaeus had initially placed it).[citation needed]
Thousands of natural inbred accessions ofA. thaliana have been collected from throughout its natural and introduced range.[16] These accessions exhibit considerable genetic and phenotypic variation, which can be used to study the adaptation of this species to different environments.[16]
A. thaliana is native to Europe, Asia, and Africa, and its geographic distribution is rather continuous from theMediterranean toScandinavia and Spain toGreece.[17] It also appears to be native in tropical alpine ecosystems in Africa and perhaps South Africa.[18][19] It has been introduced and naturalized worldwide,[20] including in North America around the 17th century.[21]
A. thaliana readily grows and often pioneers rocky, sandy, and calcareous soils. It is generally considered a weed, due to its widespread distribution in agricultural fields, roadsides, railway lines, waste ground, and other disturbed habitats,[20][22] but due to its limited competitive ability and small size, it is not categorized as a noxious weed.[23] Like most Brassicaceae species,A. thaliana is edible by humans in a salad or cooked, but it does not enjoy widespread use as a spring vegetable.[24]
Botanists and biologists began to researchA. thaliana in the early 1900s, and the first systematic description of mutants was done around 1945.[25]A. thaliana is now widely used for studyingplant sciences, includinggenetics,evolution, population genetics, and plant development.[26][27][28] AlthoughA. thaliana the plant has little direct significance for agriculture,A. thaliana the model organism has revolutionized our understanding of the genetic, cellular, and molecular biology of flowering plants.[citation needed]
The first mutant inA. thaliana was documented in 1873 byAlexander Braun, describing adouble flower phenotype (the mutated gene was likelyAgamous, cloned and characterized in 1990).[29]Friedrich Laibach (who had published the chromosome number in 1907) did not proposeA. thaliana as a model organism, though, until 1943.[30] His student, Erna Reinholz, published her thesis onA. thaliana in 1945, describing the first collection ofA. thaliana mutants that they generated usingX-raymutagenesis. Laibach continued his important contributions toA. thaliana research by collecting a large number of accessions (often questionably referred to as "ecotypes"). With the help of Albert Kranz, these were organised into a large collection of 750 natural accessions ofA. thaliana from around the world.[citation needed]
In the 1950s and 1960s, John Langridge andGeorge Rédei played an important role in establishingA. thaliana as a useful organism for biological laboratory experiments. Rédei wrote several scholarly reviews instrumental in introducing the model to the scientific community. The start of theA. thaliana research community dates to a newsletter calledArabidopsis Information Service,[31] established in 1964. The first InternationalArabidopsis Conference was held in 1965, inGöttingen, Germany.[citation needed][32]
In the 1980s,A. thaliana started to become widely used in plant research laboratories around the world. It was one of several candidates that included maize,petunia, and tobacco.[30] The latter two were attractive, since they were easily transformable with the then-current technologies, while maize was a well-established genetic model for plant biology. The breakthrough year forA. thaliana as a model plant was 1986, in whichT-DNA-mediatedtransformation and the firstclonedA. thaliana gene were described.[33][34]
Due to the small size of itsgenome, and because it isdiploid,Arabidopsis thaliana is useful for genetic mapping andsequencing — with about 157 megabase pairs[37] and fivechromosomes,A. thaliana has one of the smallest genomes among plants.[8] It was long thought to have the smallest genome of all flowering plants,[38] but that title is now considered to belong to plants in the genusGenlisea, orderLamiales, withGenlisea tuberosa, a carnivorous plant, showing a genome size of approximately 61 Mbp.[39] It was the first plant genome to be sequenced, completed in 2000 by theArabidopsis Genome Initiative.[40] The most up-to-date version of theA. thaliana genome is maintained by the Arabidopsis Information Resource.[41]
The genome encodes ~27,600protein-codinggenes and about 6,500 non-coding genes.[42] However, the Uniprot database lists 39,342 proteins in theirArabidopsis reference proteome.[43] Among the 27,600 protein-coding genes 25,402 (91.8%) are now annotated with "meaningful" product names,[44] although a large fraction of these proteins is likely only poorly understood and only known in general terms (e.g. as "DNA-binding protein without known specificity"). Uniprot lists more than 3,000 proteins as "uncharacterized" as part of the reference proteome.[citation needed]
The plastome ofA. thaliana is a 154,478 base-pair-long DNA molecule,[35] a size typically encountered in most flowering plants (see thelist of sequenced plastomes). It comprises 136 genes coding for small subunit ribosomal proteins (rps, in yellow: see figure), large subunit ribosomal proteins (rpl, orange), hypothetical chloroplast open reading frame proteins (ycf, lemon), proteins involved in photosynthetic reactions (green) or in other functions (red), ribosomal RNAs (rrn, blue), and transfer RNAs (trn, black).[36]
The mitochondrial genome ofA. thaliana is 367,808 base pairs long and contains 57 genes.[45] There are many repeated regions in theA. thaliana mitochondrial genome. The largest repeatsrecombine regularly and isomerize the genome.[46] Like most plant mitochondrial genomes, theA. thaliana mitochondrial genome exists as a complex arrangement of overlapping branched and linear moleculesin vivo.[47]
Genetic transformation ofA. thaliana is routine, usingAgrobacterium tumefaciens to transferDNA into the plant genome. The current protocol, termed "floral dip", involves simply dippingfloral buds into a solution containingAgrobacterium carrying a plasmid of interest and a detergent.[48][49] This method avoids the need fortissue culture or plant regeneration.[citation needed]
TheA. thaliana gene knockout collections are a unique resource for plant biology made possible by the availability of high-throughput transformation and funding for genomics resources. The site of T-DNA insertions has been determined for over 300,000 independent transgenic lines, with the information and seeds accessible through online T-DNA databases.[50] Through these collections, insertional mutants are available for most genes inA. thaliana.[citation needed]
Characterized accessions and mutant lines ofA. thaliana serve as experimental material in laboratory studies. The most commonly used background lines are Ler (Landsbergerecta), and Col, or Columbia.[51] Other background lines less-often cited in the scientific literature are Ws, or Wassilewskija, C24, Cvi, or Cape Verde Islands, Nossen, etc. (see for ex.[52]) Sets of closely related accessions named Col-0, Col-1, etc., have been obtained and characterized; in general, mutant lines are available through stock centers, of which best-known are the Nottingham Arabidopsis Stock Center-NASC[51] and the Arabidopsis Biological Resource Center-ABRC in Ohio, USA.[53]The Col-0 accession was selected by Rédei from within a (nonirradiated) population of seeds designated 'Landsberg' which he received from Laibach.[54] Columbia (named for the location of Rédei's former institution,University of Missouri-Columbia) was the reference accession sequenced in the Arabidopsis Genome Initiative. The Later (Landsberg erecta) line was selected by Rédei (because of its short stature) from a Landsberg population he had mutagenized with X-rays. As the Ler collection of mutants is derived from this initial line, Ler-0 does not correspond to the Landsberg accessions, which designated La-0, La-1, etc.[citation needed]
Trichome formation is initiated by the GLABROUS1 protein.Knockouts of the corresponding gene lead toglabrous plants. Thisphenotype has already been used ingene editing experiments and might be of interest as visual marker for plant research to improve gene editing methods such asCRISPR/Cas9.[55][56]
In 2005, scientists atPurdue University proposed thatA. thaliana possessed an alternative to previously known mechanisms ofDNA repair, producing an unusual pattern ofinheritance, but the phenomenon observed (reversion of mutant copies of theHOTHEAD gene to a wild-type state) was later suggested to be an artifact because the mutants show increased outcrossing due to organ fusion.[57][58][59]
The plant's small size and rapid lifecycle are also advantageous for research. Having specialized as aspring ephemeral, it has been used to found several laboratory strains that take about 6 weeks from germination to mature seed. The small size of the plant is convenient for cultivation in a small space, and it produces many seeds. Further, the selfing nature of this plant assists genetic experiments. Also, as an individual plant can produce several thousand seeds, each of the above criteria leads toA. thaliana being valued as a genetic model organism.[60]
Arabidopsis is often the model for study ofSNAREs in plants. This has shown SNAREs to be heavily involved invesicle trafficking. Zheng et al. 1999 found an arabidopsis SNARE calledAtVTI1a is probably essential toGolgi-vacuole trafficking. This is still a wide open field and plant SNAREs' role in trafficking remains understudied.[61]
TheDNA of plants is vulnerable toultraviolet light, andDNA repair mechanisms have evolved to avoid or repair genome damage caused by UV. Kaiser et al.[62] showed that inA. thaliana cyclobutane pyrimidine dimers (CPDs) induced by UV light can be repaired by expression of CPDphotolyase.
On May 12, 2022,NASA announced that specimens ofArabidopsis thaliana had been successfully germinated and grown in samples oflunar regolith. While the plants successfully germinated and grew into seedlings, they were not as robust as specimens that had been grown involcanic ash as a control group, although the experiments also found some variation in the plants grown in regolith based on the location the samples were taken from, asA. thaliana grown in regolith gathered duringApollo 12 &Apollo 17 were more robust than those grown in samples taken duringApollo 11.[63]
A. thaliana has been extensively studied as a model for flower development. The developing flower has four basic organs -sepals,petals,stamens, andcarpels (which go on to formpistils). These organs are arranged in a series of whorls, four sepals on the outer whorl, followed by four petals inside this, six stamens, and a central carpel region.Homeotic mutations inA. thaliana result in the change of one organ to another—in the case of theagamous mutation, for example, stamens become petals and carpels are replaced with a new flower, resulting in a recursively repeated sepal-petal-petal pattern.[citation needed]
Observations of homeotic mutations led to the formulation of theABC model of flower development byE. Coen andE. Meyerowitz.[64] According to this model, floral organ identity genes are divided into three classes - class A genes (which affect sepals and petals), class B genes (which affect petals and stamens), and class C genes (which affect stamens and carpels). These genes code fortranscription factors that combine to cause tissue specification in their respective regions during development. Although developed through study ofA. thaliana flowers, this model is generally applicable to other flowering plants.[citation needed]
Studies ofA. thaliana have provided considerable insights with regards to the genetics of leaf morphogenesis, particularly indicotyledon-type plants.[65][66] Much of the understanding has come from analyzing mutants in leaf development, some of which were identified in the 1960s, but were not analysed with genetic and molecular techniques until the mid-1990s.A. thaliana leaves are well suited to studies of leaf development because they are relatively simple and stable.[citation needed]
UsingA. thaliana, the genetics behind leaf shape development have become more clear and have been broken down into three stages: The initiation of theleaf primordium, the establishment ofdorsiventrality, and the development of a marginalmeristem. Leaf primordia are initiated by the suppression of the genes and proteins of class IKNOX family (such asSHOOT APICAL MERISTEMLESS). These class I KNOX proteins directly suppressgibberellin biosynthesis in the leaf primordium. Many genetic factors were found to be involved in the suppression of these class IKNOX genes in leaf primordia (such asASYMMETRIC LEAVES1,BLADE-ON-PETIOLE1,SAWTOOTH1, etc.). Thus, with this suppression, the levels of gibberellin increase and leaf primordium initiate growth.[citation needed]
The establishment of leaf dorsiventrality is important since thedorsal (adaxial) surface of the leaf is different from the ventral (abaxial) surface.[67]
A. thaliana is well suited forlight microscopy analysis. Youngseedlings on the whole, and their roots in particular, are relatively translucent. This, together with their small size, facilitates live cell imaging using bothfluorescence andconfocal laser scanning microscopy.[68] By wet-mounting seedlings in water or in culture media, plants may be imaged uninvasively, obviating the need forfixation andsectioning and allowingtime-lapse measurements.[69] Fluorescent protein constructs can be introduced throughtransformation. Thedevelopmental stage of each cell can be inferred from its location in the plant or by usingfluorescent proteinmarkers, allowing detaileddevelopmental analysis.[citation needed]
The photoreceptorsphytochromes A, B, C, D, and E mediate red light-basedphototropic response. Understanding the function of these receptors has helped plant biologists understand the signaling cascades that regulatephotoperiodism,germination,de-etiolation, andshade avoidance in plants. The genesFCA,[70]fy,[70]fpa,[70]LUMINIDEPENDENS (ld),[70]fly,[70]fve[70] andFLOWERING LOCUS C (FLC)[71][72] are involved inphotoperiod triggering of flowering andvernalization. Specifically Lee et al 1994 findld produces ahomeodomain and Blazquez et al 2001 thatfve produces aWD40 repeat.[70]
TheUVR8 protein detectsUV-B light and mediates the response to this DNA-damaging wavelength.[citation needed]
A. thaliana was used extensively in the study of the genetic basis ofphototropism,chloroplast alignment, andstomal aperture and other blue light-influenced processes.[73] These traits respond to blue light, which is perceived by thephototropin light receptors. Arabidopsis has also been important in understanding the functions of another blue light receptor,cryptochrome, which is especially important for light entrainment to control the plants'circadian rhythms.[74] When the onset of darkness is unusually early,A. thaliana reduces its metabolism of starch by an amount that effectively requiresdivision.[75]
Light responses were even found in roots, previously thought to be largely insensitive to light. While thegravitropic response ofA. thaliana root organs is their predominant tropic response, specimens treated withmutagens and selected for the absence of gravitropic action showed negative phototropic response to blue or white light, and positive response to red light, indicating that the roots also show positive phototropism.[76]
In 2000, Dr.Janet Braam ofRice University genetically engineeredA. thaliana to glow in the dark when touched. The effect was visible to ultrasensitive cameras.[77][better source needed]
Multiple efforts, including theGlowing Plant project, have sought to useA. thaliana to increase plant luminescence intensity towards commercially viable levels.[citation needed]
In 1990, Janet Braam andRonald W. Davis determined thatA. thaliana exhibitsthigmomorphogenesis in response to wind, rain and touch.[78] Four or more touch induced genes inA. thaliana were found to be regulated by such stimuli.[78] In 2002,Massimo Pigliucci found thatA. thaliana developed different patterns of branching in response to sustained exposure to wind, a display ofphenotypic plasticity.[79]
On January 2, 2019, China'sChang'e-4 lander broughtA. thaliana to the moon.[80] A smallmicrocosm 'tin' in the lander containedA. thaliana, seeds of potatoes, andsilkworm eggs. As plants would support the silkworms with oxygen, and the silkworms would in turn provide the plants with necessary carbon dioxide and nutrients through their waste,[81] researchers will evaluate whether plants successfully performphotosynthesis, and grow and bloom in the lunar environment.[80]
Thalianin is an arabidopsis roottriterpene.[82] Potteret al., 2018 findssynthesis is induced by a combination of at least 2 facts, cell-specifictranscription factors (TFs) and the accessibility of thechromatin.[82]
Understanding how plants achieve resistance is important to protect the world's food production, and the agriculture industry. Many model systems have been developed to better understand interactions between plants andbacterial,fungal,oomycete,viral, andnematode pathogens.A. thaliana has been a powerful tool for the study of the subdiscipline ofplant pathology, that is, the interaction between plants and disease-causingpathogens.[citation needed]
| Pathogen type | Example inA. thaliana |
|---|---|
| Bacteria | Pseudomonas syringae,Xanthomonas campestris |
| Fungi | Colletotrichum destructivum,Botrytis cinerea,Golovinomycesorontii |
| Oomycete | Hyaloperonospora arabidopsidis |
| Viral | Cauliflower mosaic virus (CaMV),tobacco mosaic virus (TMV) |
| Nematode | Meloidogyne incognita,Heterodera schachtii |
The use ofA. thaliana has led to many breakthroughs in the advancement of knowledge of how plants manifestplant disease resistance. The reason most plants are resistant to most pathogens is through nonhost resistance - not all pathogens will infect all plants. An example whereA. thaliana was used to determine the genes responsible for nonhost resistance isBlumeria graminis, the causal agent of powdery mildew of grasses.A. thaliana mutants were developed using themutagenethyl methanesulfonate and screened to identify mutants with increased infection byB. graminis.[84][85][86] The mutants with higher infection rates are referred to as PENmutants due to the ability ofB. graminis to penetrateA. thaliana to begin the disease process. ThePEN genes were later mapped to identify the genes responsible for nonhost resistance toB. graminis.[citation needed]
In general, when a plant is exposed to a pathogen, ornonpathogenic microbe, an initial response, known as PAMP-triggered immunity (PTI), occurs because the plant detects conserved motifs known aspathogen-associated molecular patterns (PAMPs).[87] These PAMPs are detected by specializedreceptors in the host known aspattern recognition receptors (PRRs) on the plant cell surface.
The best-characterized PRR inA. thaliana is FLS2 (Flagellin-Sensing2), which recognizes bacterialflagellin,[88][89] a specialized organelle used by microorganisms for the purpose of motility, as well as theligand flg22, which comprises the 22 amino acids recognized by FLS2. Discovery of FLS2 was facilitated by the identification of anA. thaliana ecotype, Ws-0, that was unable to detect flg22, leading to the identification of the gene encoding FLS2.FLS2 shows striking similarity to rice XA21, the first PRR isolated in 1995.[citation needed] Both flagellin andUV-C act similarly to increasehomologous recombination inA. thaliana, as demonstrated by Molinier et al. 2006. Beyond thissomatic effect, they found this toextend to subsequent generations of the plant.[90]
A second PRR, EF-Tu receptor (EFR), identified inA. thaliana, recognizes the bacterialEF-Tu protein, the prokaryotic elongation factor used inprotein synthesis, as well as the laboratory-used ligand elf18.[91] UsingAgrobacterium-mediated transformation, a technique that takes advantage of the natural process by whichAgrobacterium transfers genes into host plants, the EFR gene was transformed intoNicotiana benthamiana, tobacco plant that does not recognize EF-Tu, thereby permitting recognition of bacterial EF-Tu[92] thereby confirming EFR as the receptor of EF-Tu.
Both FLS2 and EFR use similarsignal transduction pathways to initiate PTI.A. thaliana has been instrumental in dissecting these pathways to better understand the regulation of immune responses, the most notable one being themitogen-activated protein kinase (MAP kinase) cascade. Downstream responses of PTI includecallose deposition, theoxidative burst, and transcription of defense-related genes.[93]
PTI is able to combat pathogens in a nonspecific manner. A stronger and more specific response in plants is that of effector-triggered immunity (ETI), which is dependent upon the recognition of pathogen effectors, proteins secreted by the pathogen that alter functions in the host, by plantresistance genes (R-genes), often described asa gene-for-gene relationship. This recognition may occur directly or indirectly via a guardee protein in a hypothesis known asthe guard hypothesis. The first R-gene cloned inA. thaliana wasRPS2 (resistance toPseudomonas syringae 2), which is responsible for recognition of the effector avrRpt2.[94] The bacterial effector avrRpt2 is delivered intoA. thaliana via theType III secretion system ofP. syringae pv.tomato strain DC3000. Recognition of avrRpt2 by RPS2 occurs via the guardee protein RIN4, which is cleaved.[clarification needed] Recognition of a pathogen effector leads to a dramatic immune response known as thehypersensitive response, in which the infected plant cells undergo cell death to prevent the spread of the pathogen.[95]
Systemic acquired resistance (SAR) is another example of resistance that is better understood in plants because of research done inA. thaliana. Benzothiadiazol (BTH), asalicylic acid (SA) analog, has been used historically as an antifungal compound in crop plants. BTH, as well as SA, has been shown to induce SAR in plants.The initiation of the SAR pathway was first demonstrated inA. thaliana in which increased SA levels are recognized by nonexpresser of PR genes 1 (NPR1)[96] due to redox change in the cytosol, resulting in thereduction ofNPR1. NPR1, which usually exists in a multiplex (oligomeric) state, becomes monomeric (a single unit) upon reduction.[97] When NPR1 becomes monomeric, ittranslocates to the nucleus, where it interacts with many TGAtranscription factors, and is able to induce pathogen-related genes such asPR1.[98] Another example of SAR would be the research done with transgenic tobacco plants, which express bacterial salicylate hydroxylase, nahG gene, requires the accumulation of SA for its expression[99]
Although not directly immunological,intracellular transport affectssusceptibility by incorporating - or being tricked into incorporating - pathogen particles. For example, theDynamin-related protein 2b/drp2b gene helps to move invaginated material into cells, with some mutants increasingPstDC3000 virulence even further.[100]
Plants are affected by multiplepathogens throughout their lifetimes. In response to the presence of pathogens, plants have evolved receptors on their cell surfaces to detect and respond to pathogens.[101]Arabidopsis thaliana is a model organism used to determine specific defense mechanisms of plant-pathogen resistance.[102] These plants have special receptors on their cell surfaces that allow for detection of pathogens and initiate mechanisms to inhibit pathogen growth.[102] They contain two receptors, FLS2 (bacterial flagellin receptor) and EF-Tu (bacterial EF-Tu protein), which use signal transduction pathways to initiate the disease response pathway.[102] The pathway leads to the recognition of the pathogen causing the infected cells to undergo cell death to stop the spread of the pathogen.[102] Plants with FLS2 and EF-Tu receptors have shown to have increased fitness in the population.[99] This has led to the belief that plant-pathogen resistance is an evolutionary mechanism that has built up over generations to respond to dynamic environments, such as increased predation and extreme temperatures.[99]
A. thaliana has also been used to study SAR.[103]This pathway uses benzothiadiazol, a chemical inducer, to induce transcription factors, mRNA, of SAR genes. This accumulation of transcription factors leads to inhibition of pathogen-related genes.[103]
Plant-pathogen interactions are important for an understanding of how plants have evolved to combat different types of pathogens that may affect them.[99] Variation in resistance of plants across populations is due to variation in environmental factors. Plants that have evolved resistance, whether it be the general variation or the SAR variation, have been able to live longer and hold off necrosis of their tissue (premature death of cells), which leads to better adaptation and fitness for populations that are in rapidly changing environments.[99] In the future, comparisons of thepathosystems of wild populations + theircoevolved pathogens with wild-wild hybrids of known parentage may reveal new mechanisms ofbalancing selection. Inlife history theory we may find thatA. thaliana maintains certain alleles due topleitropy between plant-pathogen effects and other traits, as in livestock.[104]
Research inA. thaliana suggests that theimmunity regulator protein family EDS1 in general co-evolved with theCCHELO family ofnucleotide-binding–leucine-rich-repeat-receptors (NLRs). Xiao et al. 2005 have shown that thepowdery mildew immunity mediated byA. thaliana'sRPW8 (which has a CCHELOdomain) is dependent on two members of this family:EDS1 itself andPAD4.[105]
RESISTANCE TO PSEUDOMONAS SYRINGAE 5/RPS5 is adisease resistance protein which guardsAvrPphB SUSCEPTIBLE 1/PBS1.PBS1, as the name would suggest, is the target ofAvrPphB, aneffector produced byPseudomonas syringae pv.phaseolicola.[106]
Ongoing research onA. thaliana is being performed on theInternational Space Station by theEuropean Space Agency. The goals are to study the growth and reproduction of plants from seed to seed inmicrogravity.[107][108] Plant-on-a-chip devices in whichA. thaliana tissues can be cultured in semi-in vitro conditions have been described.[109] Use of these devices may aid understanding of pollen-tube guidance and the mechanism of sexual reproduction inA. thaliana.[citation needed]
Researchers at theUniversity of Florida were able to grow the plant inlunar soil originating from theSea of Tranquillity.[110]
A. thaliana is a predominantly self-pollinating plant with an outcrossing rate estimated at less than 0.3%.[111] An analysis of the genome-wide pattern of linkage disequilibrium suggested that self-pollination evolved roughly a million years ago or more.[112] Meioses that lead to self-pollination are unlikely to produce significant beneficial genetic variability. However, these meioses can provide the adaptive benefit of recombinational repair of DNA damages during formation of germ cells at each generation.[113] Such a benefit may have been sufficient to allow the long-term persistence of meioses even when followed by self-fertilization. A physical mechanism for self-pollination inA. thaliana is through pre-anthesis autogamy, such that fertilisation takes place largely before flower opening.[citation needed]
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